Time after time these killers pick places where civilian guns are banned. Around the world, virtually all the attacks where at least four people have been shot to death occurred where civilians were not able to use guns to defend themselves.

Gun-control advocates claim that would-be killers don’t care about whether victims can defend themselves with a gun. After all, they reason, these killers are irrational and want to die anyway.

Elliot Rodger, who shot to death three people in Santa Barbara a couple of weeks ago, explained why he picked his target. His 141-page “Manifesto” makes it clear that he feared someone with a gun would stop him before he was able to kill enough people. He wrote:

“Another option was Deltopia, a day in which many young people pour in from all over the state to have a spring break party on Del Playa Street. I figured this would be the perfect day to attack Isla Vista, but after watching Youtube videos of previous Deltopia parties, I saw that there were way too many cops walking around on such an event. It would be impossible to kill enough of my enemies before being dispatched by those damnable cops.”

The Canadian mass shooter, Justin Bourque, also understood the importance of gun-free zones. On his Facebook page, Bourque posted comics poking fun at how gun-free zones make these crimes possible. One depicted a completely defenseless victim pleading with a man pointing a gun at him: “But wait ... there’s a GUN BAN in this city ... you can’t do this, we passed a law!” The gunman is shown thinking to himself: “Great, another one of these fruit loops.”

Bourque knew that no civilians would be able to legally carry a gun to stop him (since the 1970s, Canada has banned permitted concealed handguns).

The contrast on Sunday in Las Vegas couldn’t have been starker. Two killers shot two police officers to death. After they stole the officers’ guns and ammo, they proceeded to a nearby crowded Walmart. However, one customer, a concealed-carry permit holder, confronted the attackers and delayed them, giving other customers a chance to escape. Although the permit holder was killed, shortly after that the killers committed suicide.
All too frequently, mass killers can choose between many similar movie theaters or malls to attack. But they pick the one where victims can’t defend themselves.

The killer at the Aurora, Colo., movie theater shooting in July 2012 lived within a 20-minute drive of seven movie theaters that were showing the premier of the Batman movie. He could have simply chosen the theater that was closest to his apartment or the one with the largest auditoriums in the state. Instead, he picked the single theater where guns were banned and the victims would be defenseless.

And take Dylan Klebold, one of the two Columbine killers. He had been closely following and strongly opposed Colorado legislation that would have let citizens carry a concealed handgun. In fact, the Columbine attack occurred on the very day the bill was scheduled for final passage. Presumably, Klebold feared being stopped during his attack by someone with a weapon.

Attacks have been stopped at schools before police arrived. That includes shootings at Pearl, Miss., and Edinboro, Pa., and colleges like the Appalachian Law School in Virginia. It has happened in busy downtowns such as Memphis; in churches such as the New Life Church in Colorado Springs; in malls in Portland, Ore., and Salt Lake City; and outside an apartment building in Oklahoma.

Deterrence matters. Letting people defend themselves prevents attacks, and it also limits the harm should the attack occur. It might be one of the reasons that Michael Bloomberg and Shannon Watts both have armed bodyguards.

*John Lott is the president of the Crime Prevention Research Center and the author of “More Guns, Less Crime.”